Thermal energy storage system with input liquid kept above 650°c

ABSTRACT

A thermal energy storage system has an insulated storage container filled with a particulate earth material. A heat input conduit circuit is buried in the earth material and transfers heat from an input liquid flowing in the heat input conduit circuit to the earth material. A heat output system is operative to transfer heat from the earth material in the storage container to an external heat consumer. During operation the input liquid enters the inlet port of the heat input conduit circuit at an input operating temperature and leaves the outlet port at an output operating temperature, and the output operating temperature is above about 650° C. The input liquid remains liquid at the input and output operating temperatures under atmospheric pressure. Energy is stored at a relatively high temperature compared to the prior art, and provides increased efficiency for heat consuming processes.

This invention is in the field of thermal energy and in particularsystems for storing thermal energy, such as that generated by solarcollection.

BACKGROUND

A significant problem with solar energy development is the cyclicalnature of the energy collection due to day and night cycles, and thevariability in the amount of energy collected due to cloud cover. Formost practical uses it is necessary to have a steady supply of energy.Some uses, for example electrical power consumption, are also themselvescyclical in nature, with peak demand often twice the minimum demand.

It is therefore desirable to store thermal energy collected from the sunand draw the energy when needed. Present technology uses oil or moltensalt as a thermal energy transfer medium. Molten salt is also used as athermal energy storage medium. A molten salt presently being used is amixture of 60 percent sodium nitrate and 40 percent potassium nitrate,and has certain desirable properties. It is liquid at atmospherepressure, it provides an efficient, low-cost medium in which to storethermal energy, its operating temperatures are compatible with today'shigh-pressure and high-temperature steam turbines, and it isnon-flammable and nontoxic.

The salt melts at 221° C. and can be maintained in a liquid state in a“cold storage tank at about 280° C., then circulated through a solarcollector apparatus where the temperature is increased to about 560° C.,then it flows into a heavily insulated “hot storage tank, where it canbe stored for up to a week. When needed, hot molten salt is drawn fromthe hot storage tank and circulated through a conventional steamgenerator creating steam to operate a conventional steam turbine togenerate electrical power. It is calculated that a 100-megawatt turbinewould need tanks of about 30 feet (9.1 m) tall and 80 feet (24 m) indiameter to drive it for four hours by this design.

Conventional solar towers can increase the temperature of the moltensalt to about 560° C., however the temperature of the molten salt dropsin the steam generator such that the temperature of the generated steamis only about 280° C. Conventional steam turbines operating at thistemperature have substantially reduced efficiency when compared to ahigher temperature steam turbine operating at about 560° C.

Solar collectors are also known which can generate thermal energy atincreased temperatures of about 850° C. Such a collector is describedfor example in United States Published Patent Application Number20080184990 of Tuchelt. Increasing the temperature of a storage mediumto this increased temperature of 850° C. in the system described above,or higher, would allow steam to be generated with a temperature of about560° C., which is an ideal temperature for conventional steam turbines,and which would provide significantly improved efficiency, and thereforeincreased electrical production from collected solar energy and reducedcost of electricity.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a thermal energystorage system that overcomes problems in the prior art.

The present invention provides a thermal energy storage systemcomprising an insulated storage container substantially filled with aparticulate earth material. A heat input conduit circuit is buried inthe earth material and is configured to transfer heat from an inputliquid flowing in the heat input conduit circuit to the earth material.The heat input conduit circuit has an inlet port and an outlet port,each port defined in one of a top, bottom, and side wall of the storagecontainer. A heat output system is operative to transfer heat from theearth material in the storage container to an external heat consumer.During operation the input liquid enters the inlet port of the heatinput conduit circuit at an input operating temperature and leaves theoutlet port at an output operating temperature, and the output operatingtemperature is above about 650° C. The input liquid remains liquid atthe input and output operating temperatures under atmospheric pressure.

The high input operating temperature transfers heat energy to the earthmaterial, which is generally a poor conductor, primarily by radiation.The high storage temperature allows heat to be removed at a highertemperature than conventional systems, which higher out put temperatureprovides greater efficiency for operating steam turbines and the like.

DESCRIPTION OF THE DRAWINGS

While the invention is claimed in the concluding portions hereof,preferred embodiments are provided in the accompanying detaileddescription which may be best understood in conjunction with theaccompanying diagrams where like parts in each of the several diagramsare labeled with like numbers, and where:

FIG. 1 is a schematic top view of an embodiment of a thermal storagesystem of the present invention, and also showing a heat output systemthat is provided by a heat output conduit circuit buried in the earthmaterial of the thermal storage system;

FIG. 2 is a schematic side view of the thermal storage system and heatoutput system of FIG. 1;

FIG. 3 is a schematic top view of another embodiment of a thermalstorage system of the present invention, where the storage container isdivided horizontally and vertically into zones;

FIG. 4 is a schematic side view of the thermal storage system of FIG. 3;

FIG. 5 a schematic sectional view of a portion of the heat input conduitcircuit with an auxiliary conduit carrying an auxiliary liquid formelting the input liquid in the main conduit where the auxiliary conduitis adjacent to the main conduit;

FIG. 6 a schematic sectional view of a portion of the heat input conduitcircuit with an auxiliary conduit carrying an auxiliary liquid formelting the input liquid in the main conduit where the auxiliary conduitis inside the main conduit;

FIG. 7 a schematic sectional view of a portion of the heat input conduitcircuit with an first and second auxiliary conduits carrying a first andsecond auxiliary liquids for melting the input liquid in the mainconduit, where the first and second auxiliary conduits are adjacent tothe main conduit;

FIG. 8 a schematic sectional view of a portion of the heat input conduitcircuit with an first and second auxiliary conduits carrying a first andsecond auxiliary liquids for melting the input liquid in the mainconduit, where the first and second auxiliary conduits are inside themain conduit

FIG. 9 a schematic sectional view of a portion of the heat input conduitcircuit with an first and second auxiliary conduits carrying a first andsecond auxiliary liquids for melting the input liquid in the mainconduit, where the first auxiliary conduit is inside the main conduitand the second auxiliary conduit is inside the first auxiliary conduit;

FIG. 10 is a schematic view of a heat consumer for connection to thethermal storage system of FIG. 1, where the heat output conduit circuitis connected to an input loop of a heat exchanger, and the output loopof the heat exchanger is connected to a boiler

FIG. 11 schematically illustrates a purge and makeup regulation systemfor use with a sealed storage container containing an inert gasatmosphere.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIGS. 1 and 2 schematically illustrate an embodiment of a thermal energystorage system 1 of the present invention. The system 1 comprises aninsulated storage container 3 substantially filled with a particulateearth material 5. The earth material 5 will typically be a material suchas sand, crushed lava rock, or the like that is available in the localarea to reduce costs.

A heat input conduit circuit 7 is buried in the earth material 5 and isconfigured to transfer heat from an input liquid 9 flowing in the heatinput conduit circuit 7 to the earth material 5. The heat input conduitcircuit 7 has an inlet port 11 and an outlet port 13 defined in one of atop, bottom, and side wall of the storage container 3.

It is contemplated that the heat source 15 of the heat input liquid 9will commonly be a solar energy collector capable of raising thetemperature to the desired temperature above about 750° C. to 900° C.,however it is also contemplated that other energy sources could providethe input liquid 9 at the required temperature as well. Duringoperation, the input liquid 9 enters the inlet port 11 of the heat inputconduit circuit at an input operating temperature and leaves the outletport 13 at a lower output operating temperature. The input operatingtemperature is above about 750° C. to 900° C., and at this elevatedtemperature heat is transferred primarily by radiation. The earthmaterial 5 in the storage container 3 is a poor conductor of heat, andso in order to effectively transfer energy to the earth material, theinput liquid 9 must be at a relatively high temperature.

The energy transferred from the input liquid 9 to the earth material isproportional to the fourth power of the absolute temperature of theinput liquid 9. Thus it can be seen that at 800° C. or 1073 kelvins (K),power output of the input liquid will be 1.325X , while at 750° C. or1023 K the power output of the input liquid 9 will be only 1.095X , or83% of the power output at 800° C., and at 700° C. or 973 K the poweroutput of the input liquid 9 will be only 0.896X, or 67% of the poweroutput at 800° C. At 650° C. or 923 K the power output of the inputliquid 9 will be only 0.726X, or 55% of the power output at 800° C.

Also it can be seen that increasing the input operating temperature willincrease the rate of transfer of energy from the input liquid 9 to theearth material 5. For example at 900° C. or 1173 K the power output ofthe input liquid 9 will be 1.893X , or 142% of the power output at 800°C.

As the input liquid 9 circulates from the inlet port 11 to the outletport 13 energy moves from the input liquid 9 to the earth material 5 andthe temperature of the input liquid 9 drops from the input operatingtemperature to the output operating temperature. The rate of transfer ofenergy to the earth material 5 is much reduced when the temperaturedrops and it is contemplated that the temperature of the input liquid 9in the heat input conduit circuit 7 should not fall below about 650° C.or insufficient heat transfer will occur to heat the earth material 5.

The temperature of the input liquid 9 falls generally proportional tothe time it is in the heat input conduit circuit 7. The outputtemperature can thus be controlled by increasing or decreasing the rateof flow of the input liquid through the heat input conduit circuit 7.Thus for example where the input operating temperature is 800° C., theinput liquid may be circulated at a rate of X gallons per minute toresult in an output operating temperature of 650° C., but where theinput operating temperature is only 750° C., the input liquid will needto be circulated at a higher rate of X+ gallons per minute to result inthe desired output operating temperature of 650° C.

A heat output system is operative to transfer heat from the earthmaterial 5 in the storage container 3 to an external heat consumer 21,such as a boiler or like apparatus that will utilize the heat energy.Similarly to the input mechanism described above, and again because theearth material 5 is a poor conductor, the heat is drawn out of the earthmaterial also primarily by radiation. While the earth material 5 is apoor conductor, it is also very cheaply available in the very largequantities contemplated as necessary for electric power generation orlike large scale uses, and in the system 1 of the present inventionusing the high temperature input liquid 9, an economical storage systemfor heat energy is provided, and available to be drawn out for varioususes.

It is contemplated that the heat output system would typically be a heatoutput conduit circuit 17 with an output liquid 19 flowing therethrough,and arranged similar to the heat input conduit circuit 7 to absorb heatenergy radiated from the heated earth material 5. The temperature of theoutput liquid 19 will be significantly lower than the input liquid 9,and so the output liquid 19 will typically be a different liquid thanthe input liquid 9 with a lower melting temperature. It is alsocontemplated that the heat output system could comprise heat pipes orother systems known in the art to move heat energy from the earthmaterial 5 to a heat consuming process 21 such as a boiler.

The input liquid 9 is selected so that it will remain liquid at theinput and output operating temperatures under atmospheric pressure. Onepossible choice that has several advantages is aluminum, with a meltingpoint of 660° C. and a boiling point above the operating temperaturerange. It is relatively economical and very light weight therebyreducing the energy needed to circulate it. It is also contemplated thatin order to provide a significant portion of the world's energy fromsolar power, a great deal of this input liquid will be required, andaluminum also has the advantage of being very plentiful, as it is thethird most abundant element in the earth's crust at about 8.1%.

Another possible choice for the input liquid 9 is sodium, which has amelting point of just 98° C. and an atmospheric boiling point 883° C.which is above the contemplated operating temperatures. Sodium is alsovery light weight, inexpensive, and plentiful, but has the majordrawback that it becomes explosive when mixed with water and poses asignificant danger in the event of a failure. A further possible choicefor the input liquid 9 is tin, which has a melting point of 232° C. anda boiling point also above the operating temperature range, but tin ismore costly, and less plentiful. It is contemplated other materials maybe found to be suitable as well. Tin and sodium may be suitable for useas the output liquid 19, as both have a relatively low meltingtemperature.

Thus the only pressure in the heat input conduit circuit 7 is thatexerted by the pumps circulating the input liquid. At the high operatingtemperatures of the present system 1, the metal of the pipes forming theheat input conduit circuit 7 is susceptible to failure, and by keepingthe pressures inside low, the risk of failure, leakage, and the like isreduced. Operating at low pressure also allows for the use of lesscostly conduit materials than those required for both high temperatureand high pressure operation.

The illustrated container 3 is formed by an inner wall and an outer wallwith an insulation space 23 between the inner and outer walls that isfilled with an insulating material.

FIGS. 3 and 4 schematically illustrate a different embodiment of thethermal energy storage system 101 of the present invention where thestorage container 103 is buried in the ground 102 such that the groundsupports walls of the storage container 103. This arrangementsignificantly reduces the structural strength required of the containerwalls. Also the storage container 103 is a cube with equal dimensionsfor length, width, and height, and providing a maximum volume of earthmaterial 105 with a minimum wall surface area, thus reducing heat lossthrough the walls. The storage container may also be cylindrical inshape as in the embodiment of FIGS. 1 and 2. This cylindrical shapewould be particularly applicable for an above ground installation inwhich the weight of the earth material 105 would want to naturally formthis shape. It also may be possible in some areas to dig the holerequired for the storage container 103 by removing suitable earthmaterial 105.

In the system 101, the heat input conduit circuit 107 from the source115 is divided vertically and horizontally into eight substantiallycubic input zones 129, as schematically illustrated by dotted lines 131.By manipulating valves 133, the input conduit circuit 107 can beconfigured such that the flow of input liquid 109 can be directedthrough selected input zones 129, or combinations of the input zones129, or through all the input zones 129 at once to transfer heat toearth material in corresponding earth material zones 135.

The heat output system 117 may likewise be operative to transfer heatfrom selected earth material zones 135, or combinations of the earthmaterial zones 135, or all the earth material zones 135 to an externalheat consumer 121.

Thus with the system 101, the output system 117 would draw thetemperature of the earth material in a zone 135 down by a desiredamount, for example 50° C., and then the output system 117 would bechanged to draw from a different zone 135. Similarly the heat inputconduit circuit 107 could be configured to circulate input liquid 109through each zone 129 separately or in combination, depending on theamount of heat available from the source 115 and the heat being drawnout by the heat output system 117.

In either system 1 or 101, but referring for convenience to system 1 ofFIGS. 1 and 2, if the temperature of the input liquid falls below itsmelting point the liquid will solidify in the conduits of the heat inputconduit circuit 7. For example where the input liquid is aluminum, whenthe temperature thereof drops to 660° C., the input liquid will turn toa solid. It is thus desirable to provide a system for reheating theinput liquid to the melting point. Where the source 15 of the heat inputliquid 9 is a solar collection system, it is contemplated that,particularly where the input liquid is aluminum with a higher meltingpoint compared to tin or sodium, the input liquid will solidify at leastperiodically in some portions of the heat input conduit circuit 7 duringthe night or during cloudy periods.

Pumps, valves, junctions, and like areas of the heat input conduitcircuit 7 are typically heated to the melting point of the input liquid9 by electrical heaters. The entire heat input conduit circuit 7 couldalso be heated by electricity however it is desirable to be able to heatlengthy portions of the heat input conduit circuit 7, such as thoseburied in the earth material 5 or that connect the storage container 3to the heat source 15, directly with heat from the heat source 15.

FIG. 5 schematically illustrates a cross-section of a portion of theheat input conduit circuit 7 that comprises a main conduit 41 and anauxiliary conduit 43 arranged in proximity to the main conduit 41. Inoperation the input liquid 9 flows in the main conduit 41, and anauxiliary liquid 45 flows in the auxiliary conduit, such that heattransfers from the auxiliary liquid 45 to the input liquid 9. Theauxiliary liquid is selected to have a melting temperature that is lessthan a melting temperature of the input liquid 9.

In operation then if the temperature of the portion of the heat inputconduit circuit 7 drops below the melting temperature of the inputliquid, the auxiliary will remain liquid until the temperature of theauxiliary liquid also drops below its melting temperature, which will bemuch lower, and so will not often be encountered unless the heat sourcegoes cold for an extended period. While the auxiliary liquid 45 isliquid, it can be circulated through auxiliary conduit 43 to the heatsource 15 to raise the temperature thereof well above the melting pointof the input liquid 9 and the heat from the auxiliary liquid 45circulating in the auxiliary conduit 43 will be transferred to the mainconduit 41 to melt the input liquid 9. In order to avoid buildingpressure in the auxiliary conduit 43, the auxiliary liquid 45 can beselected to have a boiling temperature at atmospheric pressure that isgreater than the input operating temperature.

FIG. 5 shows a heat input conduit circuit portion 7 where the auxiliaryconduit 43 is beside the main conduit 41, and FIG. 6 shows an optionalarrangement where the auxiliary conduit 43 is inside the main conduit41.

The auxiliary liquid could be a metal alloy with a low melting point,such as Field's metal with a melting temperature of 62° C. or Woodsmetal with a melting temperature of 70° C. Field's metal may be moresuitable as same contains no harmful lead or cadmium. The auxiliaryliquid 45 may be relatively costly compared to the input liquid 9, butcould be drained from the auxiliary conduit 43 and used in differentheat input conduit circuits at different times as required, so it iscontemplated that the cost will not be prohibitive.

While it is contemplated that the auxiliary liquid 45 will not oftenfall below its melting temperature, means should generally be providedto also melt the auxiliary liquid if it does solidify. FIGS. 7-9schematically illustrate a heat input conduit circuit comprising themain conduit 41, and two auxiliary conduits 43A, 43B.

The first auxiliary conduit 43A is arranged in proximity to the mainconduit 41 such that heat is transferred from a first auxiliary liquid45A flowing in the first auxiliary conduit 43A to the input liquid 9 inthe main conduit 41, and the second auxiliary conduit 4313 is arrangedin proximity to the first auxiliary conduit 43A such that heat istransferred from a second auxiliary liquid 45B flowing in the secondauxiliary conduit 43B to the first auxiliary liquid 45A. The meltingtemperature of the first auxiliary liquid 45A is less than a meltingtemperature of the input liquid 9 and, in turn the melting temperatureof the second auxiliary liquid 45B is less than a melting temperature ofthe first auxiliary liquid 45A.

The second auxiliary liquid 45B can conveniently be selected to alsohave a melting point lower than ambient temperature at the location ofthe system. Thus if the entire system goes cold, the second auxiliaryliquid 45B will remain liquid and can be circulated through the heatsource to raise the temperature thereof to a level above the meltingpoint of the first auxiliary liquid 45A, which in turn is circulatedthrough the heat source as described above to melt the input liquid 9.

The second auxiliary liquid 45B conveniently can be water. The meltingtemperature of the metal alloy of first auxiliary liquid 45A can beselected to be below the boiling temperature of the water at atmosphericpressure, such that the water of the second auxiliary liquid 45B in thesecond auxiliary conduit 43B is not under pressure.

If the melting temperature of the metal alloy of first auxiliary liquid45A is above the boiling temperature of the water at atmosphericpressure, some increased pressure could be maintained in the secondauxiliary conduit 43B to increase the boiling temperature of the waterin the second auxiliary conduit 43B. As schematically illustrated inFIG. 7, a valve 47 can be provided to selectively release pressure fromthe second auxiliary conduit 43B such that the water in the secondauxiliary conduit 43B simply boils out of the secondary auxiliaryconduit 43B as the temperature in the heat input conduit circuit 7rises.

FIG. 7 schematically illustrates a heat input conduit circuit 7comprising the main conduit 41, and two auxiliary conduits 43A, 43Bplaced adjacent to the main conduit 41. In the embodiment of FIG. 8, thetwo auxiliary conduits 43A, 43B are placed inside the main conduit 41,and in FIG. 9 the second auxiliary conduit 43B is inside the firstauxiliary conduit 43A which in turn is inside the main conduit 41. It iscontemplated that placing the auxiliary conduits 43A, 43B inside themain conduit 41 may make a convenient package and facilitateinstallation and/or maintenance in the earth material filled storagecontainer.

FIG. 10 schematically illustrates a heat consumer 21 for connection tothe heat output system of the energy storage system 1 of FIGS. 1 and 2that includes a heat output conduit circuit 17 with an output liquid 19flowing therethrough. The heat output conduit circuit 17 is connected toa heat exchanger 51 which transfers heat from the output liquid 17 to asecondary liquid 53 from the heat exchanger 51 to a boiler 55. The heatexchanger 51 maintains separation between the output liquid 19 and theboiler 55 which contains water. The separation allows the output liquidto be more safely provided by sodium, which is relatively inexpensive,and has a low melting temperature of 98° C. With the sodium flowing asthe output liquid in the input loop of the heat exchanger 51, and tin orsome like non-hazardous as the secondary liquid 53 flowing in the heatoutput loop of the heat exchanger 51 to the boiler 55, there is littlerisk of contact between the sodium in the heat output conduit circuit 17and the water in the boiler 55.

With the earth material 5 in the storage container 3 at a temperature ofabout 750° C., it is calculated that the boiler 55 could provide steamat a temperature of about 550° C. which is an efficient temperature foroperating a modern conventional steam turbine to produce electricalpower. The temperature of the output liquid 19 flowing to the heatconsumer 21 can be controlled to a desired temperature, for example byadjusting a bypass mixing valve 57, or by varying the rate of flow ofoutput liquid 19 through the heat output conduit circuit 17 with avariable output pump 59.

Thus in a typical energy storage system 1 of the present invention, theinput liquid 9 is aluminum with a melting temperature of 660° C., thefirst auxiliary liquid 45A is a metal allow such as Field's metal with amelting temperature of 62° C., and the second auxiliary liquid 45B iswater. The first and second auxiliary conduit may remain empty until itis necessary to melt the aluminum input liquid. Initially at start up,the heat input conduit circuit 17 will be preheated with steam or thelike to a temperature approaching 660° C. and then the molten aluminumwill be pumped through and substantially fill the heat input conduitcircuit 7. From this point, depending on the operation of the heatsource 15, the liquid aluminum 9 will circulate until the temperaturethereof drops below 660° C. The Field's metal 45A will remain liquid ifpresent until the temperature drops below 62° C. The water 45B will notusually be present in the auxiliary conduit 43B until it is needed toheat the Field's metal 45A.

It is calculated that a volume of about 14,700 cubic meters of earthmaterial would provide sufficient thermal energy storage for a 20megawatt electrical turbine. The storage container 3 would then be acube about 11.4 meters on each side, with a heat input conduit circuitburied therein with conduits of about five centimeters (cm) in diameterspaced about 25 cm apart in a grid throughout the earth material 5filing the storage container 3.

The container 3, and insulation space 23 if desired, can also be sealedand filled with a substantially inert gas atmosphere of nitrogen, carbondioxide, helium, argon, or the like which will keep the earth materialdry and reduce corrosion of the material of the container walls. Asuitable wall material is stainless steel, which will resist corrosion.Where the storage container 3 and insulation space 23 is sealed, asschematically illustrated in FIG. 11, the pressure inside them will riseand fall as the temperature varies. To avoid excessive expanding andcollapsing pressures being exerted on the container walls, a purge andmakeup regulation system 61 is operative to selectively release inertgas from the storage container 3 and insulation space 23 through a vent63 to the ambient atmosphere, and add inert gas from a pressurized gascontainer 65 to the storage container 3 and insulation space 23, tomaintain atmospheric equilibrium therein during thermal expansion andcontraction of the inert gas atmosphere as temperature changes

The foregoing is considered as illustrative only of the principles ofthe invention. Further, since numerous changes and modifications willreadily occur to those skilled in the art, it is not desired to limitthe invention to the exact constriction and operation shown anddescribed, and accordingly, all such suitable changes or modificationsin structure or operation which may be resorted to are intended to fallwithin the scope of the claimed invention.

1. A thermal energy storage system comprising: an insulated storagecontainer substantially filled with a particulate earth material; a heatinput conduit circuit buried in the earth material and configured totransfer heat from an input liquid flowing in the heat input conduitcircuit to the earth material, the heat input conduit circuit having aninlet port and an outlet port, each port defined in one of a top,bottom, and side wall of the storage container; a heat output systemoperative to transfer heat from the earth material in the storagecontainer to an external heat consumer; wherein during operation theinput liquid enters the inlet port of the heat input conduit circuit atan input operating temperature and leaves the outlet port at an outputoperating temperature; wherein the output operating temperature is aboveabout 650° C.; and wherein the input liquid remains liquid at the inputand output operating temperatures under atmospheric pressure.
 2. Thesystem of claim 1 wherein the earth material comprises one of sand andcrushed lava rock.
 3. The system of claim 1 wherein the storagecontainer is sealed and contains a substantially inert gas atmospherewith the earth material, and wherein a purge and makeup regulationsystem is operative to selectively release inert gas from the storagecontainer and add inert gas to the storage container to maintainatmospheric equilibrium therein during thermal expansion and contractionof the inert gas atmosphere as temperature changes.
 4. The system ofclaim 3 wherein the storage container is formed by an inner wall and anouter wall with an insulation space between the inner and outer walls,and wherein the insulation space contains the same substantially inertgas atmosphere, and wherein a purge and makeup regulation system isoperative to selectively release inert gas from the insulation space andadd inert gas to the insulation space to maintain atmosphericequilibrium therein during thermal expansion and contraction of theinert gas atmosphere as temperature changes.
 5. The system of claim 3wherein the substantially inert gas atmosphere comprises at least one ofnitrogen, carbon dioxide, helium, and argon.
 6. The system of claim 1wherein walls of the storage container comprise stainless steel.
 7. Thesystem of claim 1 wherein the storage container is buried in the groundsuch that the ground supports walls of the storage container.
 8. Thesystem of claim 1 wherein the heat input conduit circuit is divided intoat least first and second input zones and is configured such that theflow of input liquid can be directed through one of the first inputzone, the second input zone, and both input zones to transfer heat toearth material in one or both corresponding first and second earthmaterial zones.
 9. The system of claim 8 wherein the heat output systemis operative to transfer heat from the earth material in one of thefirst earth material zone, the second earth material zone, and bothearth material zones to the external heat consumer.
 10. The system ofclaim 1 wherein at least one conduit of the heat input conduit circuitcomprises a main conduit and at least one auxiliary conduit arranged inproximity to the main conduit, wherein the input liquid flows in themain conduit, and wherein an auxiliary liquid flows in the at least oneauxiliary conduit such that heat transfers from the auxiliary liquid tothe input liquid, and wherein a melting temperature of the auxiliaryliquid is less than a melting temperature of the input liquid.
 11. Thesystem of claim 10 wherein the auxiliary conduit is inside the mainconduit.
 12. The system of claim 10 comprising first and secondauxiliary conduits, wherein the first auxiliary conduit is arranged inproximity to the main conduit such that heat is transferred from a firstauxiliary liquid flowing in the first auxiliary conduit to the inputliquid, and wherein the second auxiliary conduit is arranged inproximity to the first auxiliary conduit such that heat is transferredfrom a second auxiliary liquid flowing in the second auxiliary conduitto the first auxiliary liquid, and wherein a melting temperature of thefirst auxiliary liquid is less than a melting temperature of the inputliquid and wherein a melting temperature of the second auxiliary liquidis less than a melting temperature of the first auxiliary liquid. 13.The system of claim 12 wherein the first and second auxiliary conduitsare inside the main conduit.
 14. The system of claim 13 wherein thesecond auxiliary conduit is inside the first auxiliary conduit.
 15. Thesystem of claim 10 wherein a boiling temperature of the auxiliary liquidat atmospheric pressure is greater than the input operating temperature.16. The system of claim 12 wherein a boiling temperature of the firstauxiliary liquid at atmospheric pressure is greater than the inputoperating temperature.
 17. The system of claim 12 wherein the secondauxiliary liquid has a melting point lower than ambient temperature at alocation of the system.
 18. The system of claim 17 wherein the secondauxiliary liquid is water, and the first auxiliary liquid is a metalalloy.
 19. The system of claim 18 wherein the melting temperature of themetal alloy is below a boiling temperature of the water in the secondauxiliary conduit.
 20. The system of claim 19 wherein pressure ismaintained in the second auxiliary conduit to increase the boilingtemperature of the water in the second auxiliary conduit.
 21. The systemof claim 18 comprising a valve operative to selectively release pressurefrom the second auxiliary conduit such that the water in the secondauxiliary conduit boils out of the secondary auxiliary conduit.
 22. Thesystem of claim 1 wherein the heat output system comprises a heat outputconduit circuit buried in the earth material and configured to transferheat from the earth material in the storage container to an outputliquid flowing in the heat output conduit circuit.
 23. The system ofclaim 22 wherein a temperature of the output liquid delivered to theexternal heat consumer is controlled by adjusting one of a bypass mixingvalve and a variable output pump circulating the output liquid throughthe heat output conduit circuit.
 24. The system of claim 22 wherein theheat output conduit circuit is connected to circulate through an inputloop of a heat exchanger and wherein an output loop of the heatexchanger is connected to a boiler, and wherein the output liquid in theheat output conduit circuit and the input loop of a heat exchanger issodium, and wherein a boiler liquid in the output loop of the heatexchanger is not sodium.
 25. The system of claim 1 wherein the inputliquid is one of aluminum, sodium, and tin.